Today, active studies or technological developments are in progress to improve transmission rates in mobile communication systems. Among them, for example, there is a method of using wider band signals to improve transmission rates in the mobile communication system. To transmit such a wider band signal, quasi-millimeter waves with higher frequencies than those of microwaves have to be used. However, using such high-carrier frequency signals sees an increase in propagation loss. It may further lead to a problem, such as reduction of a service area to provide mobile communication services or significant degradation of transmission quality.
Therefore, as a technology to compensate for the propagation loss, for example, antenna array technologies that secure line quality by using array gain are attracting attention. One of the antenna array technologies is disclosed in JP 2008-205645.
In order to attain greater array gain, quite many antenna elements, also called ‘array elements’, are required compared with a conventional phased array antenna. However, for example, in a case where a frequency converter and an analog-to-digital converter (A/D converter) are installed for each array element, and a signal reproduction process or an orientation (phase) control process is to be performed based on a signal received at each array element, a problem arises that the scale of a circuit or an apparatus becomes significantly larger.
Only if an analog circuit for processing a signal with an intermediate frequency handles combination of signals received by array elements, it is possible to reduce the scale of the circuit or apparatus. However, any sophisticated method (for example, with higher accuracy) in handling signal detection or orientation control cannot be used when the analog circuit combines signals received by array elements. In this case, enhancement of transmission quality cannot be attempted sufficiently.
To address these problems, JP 2008-205645 suggests a method including grouping a plurality of array elements that constitutes a phased array antenna, combining signals received by array elements for each sub-array grouped with the array elements, and handling a process of signal reproduction or orientation control. With the method, it is possible to reduce the scale of an associated circuit or apparatus or utilize more sophisticated scheme, compared with a case that uses a frequency converter or an A/D converter.
Specifically, in the method suggested by JP 2008-205645, a communication device for handling orientation control corrects amplitude or phase based on a known reference transmit signal (for example, equivalent to a training signal) transmitted from a transmitting device. However, since the method is to correct the amplitude or phase based on the reference transmit signal equivalent to a training signal, it cannot be said that the method helps to improve accuracy of orientation control for a signal representing actual data, such as user data.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.